TGXL and Power Supply loud hum

Randy Hollingsworth

This is a bit of an odd one. For several weeks the Astron RS-35M power supply used with my Flex Radio 6500 has developed a very loud hum. I assumed it was a PS issue, replaced the likely components in the PS with no change to the hum. I have been running my PGXL off a different power supply via a West Mountain Rig Runner. When I turned off the Power Supply feeding the PGXL, the hum stopped. I then turned the PS back on then turned off the rig runner and the hum again stopped. I then turned the rig runner back on and pulled out the power pole connectors one by one till I found the one that stopped the hum. It was the TGXL. I then tried running the TGXL and the 6500 off the same RS-35M supply, again it made no difference.

So, When both the 6500 and TGXL are on, the RS-35M has a very loud hum. If you turn off the TGXL with the 6500 running, the hum disappears. If you turn off the 6500 and with the TGXL running, the hum disappears.

I am at a loss as to explain what the cause could be. Both the 6500 and TGXL are grounded to a common ground, and other than the RF cables running through each, there is no physical connection between the units. Any suggestions on what to try to eliminate the hum would be very appreciated.

Mike-VA3MW

Randy

I assume you changed the Power Supply in the PGXL?

It sounds like you have an AC ground loop. I would check your sockets and make sure that you don't have a Neutral / HOT swap. There are tools you can use to check that.

This could happen if you are running the PGXL at 120VAC.

Or, how are you grounding equipment? You could use an AC voltmeter to compare the ground voltages between the Radio, TGXL, PGXL and other equipment. You should read 0VAC. Also, disconnect all other equipment from the radio as a test and minimize the station until you isolate the problem.

These are all areas I would look into.